Power circuit breakers, in particular low-voltage power circuit breakers, are automatic electromagnetic circuit breakers in the event of a short circuit. The way in which they function corresponds in principle to the way in which line circuit breakers function. They are usually equipped with a thermal and a magnetic release and therefore have the same structural elements as line circuit breakers. However, they are designed for higher rated currents, and in addition the releases are adjustable, sometimes separately, by power circuit breakers, which is different than in the case of line circuit breakers. In the low-voltage sector, the breakers are also used as motor circuit breakers.
The object of the power circuit breaker is to protect downstream installations, in particular three-phase motors, from damage as a result of overload or short circuit. The power circuit breaker should disconnect these currents in conjunction with the line protection devices. If gas is located between the two poles, this gas is ionized by virtue of the flashover in the case of a correspondingly high voltage difference between the poles, and a self-maintaining gas discharge, which is also referred to as an arc, is formed. This plasma not only continues to conduct current, but also reduces the life of the component part and, in the case of high currents, can even destroy the switch. In contrast to disconnectors, power circuit breakers are designed such that the arc produced during opening of the switching contacts is quenched and therefore the current flow is interrupted quickly and without any damage to the switch.
A particular problem associated with power circuit breakers with a high switching capacity, in particular up to 100 kA at rated currents of up to 80 A, consists in that, in the case of such large short circuits, the loading on the chamber walls, i.e. in particular on the lower part of the power circuit breaker owing to the high development of pressure, is very high. The housing walls can in the case of such tripping operations bend outwards or result in a rupture in the upper part of the power circuit breaker. In the worst case scenario, parts of the upper part are broken away.
In this regard, WO 01/33595 A1 describes an electrical circuit breaker, in particular a motor circuit breaker, comprising a housing including a thermosetting plastic, a switching contact arrangement, a tripping unit with at least one bimetallic-element release, a tripping link which acts on a switching mechanism and can be actuated by the bimetallic element and a parts mount consisting of insulating material for various contact and connection parts of the tripping unit which can be formed on this parts mount.
In the case of this electrical circuit breaker, provision is made for the preassemblable contact and connection parts of the tripping unit to be adhesively bonded into the housing or a housing part, with the result that the fastening of these preassemblable contact and connection parts in the housing takes place without any additional connections. For this, housing adhesive-bonding pockets are provided which are filled with adhesive material. Pins of the tripping unit protrude into these adhesive-bonding pockets and can be adhesively bonded in the adhesive-bonding pockets. By virtue of the permanent adhesive bonding, the bimetallic element position is kept stable. Thermal and mechanical stresses are considerably reduced by the use of the adhesive and by the adhesion process, while the thermal stability and dimensional stability are ensured.